Android开发：如何使用onKeyUp？

正确的方法是使用TextWatcher类。

EditText tv_filter = (EditText) findViewById(R.id.filter);TextWatcher fieldValidatorTextWatcher = new TextWatcher() {        @Override        public void afterTextChanged(Editable s) {        }        @Override        public void beforeTextChanged(CharSequence s, int start, int count, int after) {        }        @Override        public void onTextChanged(CharSequence s, int start, int before, int count) { if (filterLongEnough()) {     populateList(); }        }        private boolean filterLongEnough() { return tv_filter.getText().toString().trim().length() > 2;        }    };    tv_filter.addTextChangedListener(fieldValidatorTextWatcher);